This invention relates to radar systems that transmit a beam of high frequency energy in a scanning mode to identify the presence, locus, motion, and characteristics of scatters in a region of space.
It is a problem in the field of radar systems, and weather radar systems in particular, to implement an inexpensive system that collects sufficient data to provide accurate information to the users relating to the presence, locus and characteristics of scatters in a region of space, in a short period of time. Radar systems can be characterized in terms of the basic system architecture as either monostatic radar systems which use a single transmitter and receiver or bistatic radar network systems which use a single radar transmitter and a plurality of receivers, at least one of which is located remotely from the transmitter site.
Included in the field of monostatic radar systems are the standard narrow beam radar systems which transmit a single narrow beam of high frequency radiation, then receive signals, which constitute components of this narrow beam that have been reflected off scatterers located in the path of the beam. These systems usually include a mechanically driven antenna to execute a predetermined scan pattern that covers a predetermined volume of space. The scanning speed is limited by the ability to obtain independent meteorological samples using a single frequency and by the ability to mechanically move a large antenna, thereby preventing these systems from both scanning extremely rapidly and frequently revisiting particular regions of space. To increase the accuracy of the data produced by the narrow beam radar systems, expensive rotating high gain antennas are used. As a result, the cost of implementing, operating, and maintaining such systems is high. Furthermore, the accuracy of the data produced is adversely affected by the infrequent scan pattern of the rotating antenna. These narrow beam radar systems, when used as a weather radar, collect data that is indicative of only the radial component of the wind field present in the predetermined volume of space.
Included in the field of monostatic radar systems are the broad beam radar systems which transmit a single broad beam of high frequency radiation. These systems receive a plurality of signals, comprising the radiation that is reflected off a plurality of scatters located in the broad beam of the transmitted beam, using a receiving antenna or antennas that is/are sensitive to radiation from particular directions more than others. These broad beam radar systems can include a mechanically driven antenna to execute a predetermined scan pattern that covers a predetermined volume of space. The sensitivity of these systems is low due to the broad beam transmission. These systems are also adversely affected by the fact that radiation is received from outside the narrowly defined directions defined by the receiving antennas. These broad beam radar systems, when used as a weather radar, also collect data that is indicative of only the radial component of the wind field present in the predetermined volume of space.
An alternative to monostatic radar systems are the bistatic radar networks which use a single radar transmitter and a plurality of passive, low-gain receivers, at least one of which is located remotely from the transmitter site, such as is disclosed in U.S. Pat. No. 5,410,314, U.S. Pat. No. 5,469,169, U.S. Pat. No. 5,471,211. In such a network, the transmitter produces a xe2x80x9cpencil beamxe2x80x9d of high frequency energy, which is reflected off scatterers as the rotating antenna scans the predetermined volume of space. The reflected radial component of the beam is received by a receiver located at the transmitter site, while other components of the reflected beam are received at other receivers located remote from the transmitter site. The bistatic radar network has the advantage of receiving back scattered reflections indicative of the radial component of the scatterer motion as well as other components, which enable the network to simply produce a three-dimensional determination of the characteristics of the scatterers. This radar network is relatively inexpensive due to the use of the plurality of passive, low-gain receivers, but does require the use of a transmitter that is closely synchronized with the plurality of remotely located receivers to enable the receivers to track the transmitted pulses by working from the same time base and scan pattern as the transmitter. The synchronization can be accomplished on a less than pulse basis, if the transmitter frequency, pulse rate and scan pattern are all known and immutable. However, any irregularities in these criteria result in the receivers being incapable of computing the location of the scatterers, since the origin of the pulses are not known.
The above described problems are solved and a technical advance is achieved by the present bistatic radar network having an incoherent transmitter for determining the presence, locus, motion, and characteristics of scatterers in a predefined space. The incoherent transmitter generates pulses of high frequency energy that vary in frequency and/or phase. The bistatic radar network having an incoherent transmitter uses a scanning beam antenna located at the transmitter to transmit a focused beam of high frequency energy into a predefined space, with the transmitted beam comprising a series of pulses, each pulse in the series of pulses having a varying frequency, phase, pulse origination time and direction of propagation as it is emanated from the antenna. The transmitter also includes apparatus for determining pulse origination data comprising: frequency, phase, pulse origination time and direction of propagation, for each of the pulses in the transmitted beam emanating from the antenna, where the antenna is scanned in a predetermined scan pattern in at least an azimuthal direction. The bistatic network also includes at least one receiver, located at a site remote from the transmitter and includes apparatus for generating pulse component receipt data indicative of receipt of components of the pulses that are contained in the transmitted beam that are reflected from scatterers in the predefined space, and a processor, responsive to receipt of the pulse origination data from the transmitter and the pulse component receipt data, for generating scatterer location data indicative of presence, locus, motion, and characteristics of scatterers in the predefined space.